1. Field of the Invention
The present invention relates to a ladder filter including a plurality of elastic wave resonators and to a duplexer including the ladder filter as a transmission filter.
2. Description of the Related Art
In the related art, ladder surface acoustic wave filters are widely used in transmission filters of duplexers of cellular phone devices and so forth. An example of such a duplexer is disclosed in Japanese Unexamined Patent Application Publication No. 2013-168996. In Japanese Unexamined Patent Application Publication No. 2013-168996, a series-arm resonator having the largest electrostatic capacity among a plurality of series-arm resonators of a ladder surface acoustic wave filter is arranged at the side of a transmission terminal.
As described in Japanese Unexamined Patent Application Publication No. 2013-168996, the power durability can be made high by making the electrostatic capacity of the series-arm resonator closest to the transmission terminal, that is, the input terminal, the highest. However, there is a problem in that when the electrostatic capacity becomes large, electrical characteristics are degraded.